Analog or digital information may be communicated to a remote receiver using a variety of communication theory techniques. A typical transmission system includes a transmitter, a communication channel, and a receiver. The transmitter converts the analog or digital information into a form that is suitable for transmission over the communication channel. The receiver recreates the original information from the transmitted signal. The communication channel may be any transmission medium such as wire, optical fiber, or merely free space in which the signals are transmitted as an electromagnetic wave (e.g., radio and television signals).
In a typical wireless communication system, a data signal that includes the information is modulated with a carrier signal and transmitted into free space with an antenna. The receiving system has an antenna and receiver that are tuned to the carrier frequency. The receiving system demodulates the received signal and extracts the data signal. The antenna that is used in the receiving system is usually closely tuned to the carrier frequency.
In portable devices, the physical dimensions of the antenna may be very small. In one portable device, an antenna may be formed in a wristband for a watch. A wristband antenna may be formed from a loop of wire that circumscribes the wrist of the wearer. Since the circumference of each wearer's wrist may be different, the resonant frequency of the antenna will also vary.